In general, non-polar plastics such as polyethylene, polypropylene and the like have poor dyeability, ink receptivity, plating and coating properties and adhesion characteristics.
In order to improve these properties of the plastics, incorporation of inorganic fillers in the plastics, physical or chemical treatments or plastic articles, e.g., surface treatments such as chemical etching using acid, corona discharge treatment, flame treatment, plasma jet treatment, etc., surface-coarsening using sandpaper, etc., application of primers, etc., have heretofore been conducted.
These techniques, however, have disadvantages in that expensive apparatus and complicated operations are needed, the plastic articles to be treated are limited in their shapes and sizes, care must be taken in handling the already molded plastic articles and it is difficult to effect a uniform treatment.
On the other hand, a method of introducing polar groups into a polypropylene resin by reacting it with maleic anhydride, for example, to improve the adhesion characteristics and dyeability thereof is described in Japanese Patent Publications Nos. 27421/1968 and 15422/1969. This method, however, has failed to sufficiently achieve the expected results since it is difficult to introduce a large amount of the polar groups.